1. Field of the Invention
The present invention relates to a structure of a flat speaker. More particularly, the present invention relates to an assembly structure of a flat speaker.
2. Description of Related Art
Two most direct sensory responses of mankind are visual system and hearing system. Therefore, scientists have been dedicated to develop devices or system techniques related to the visual system and the hearing system. Presently, electroacoustic speakers are mainly classified into direct and indirect radiation speakers, and according to driving methods thereof, the speakers are mainly classified into moving-coil, piezoelectric and electrostatic speakers. Whatever the speaker is, main components thereof include electrodes, a vibrating film and chambers.
Presently, the moving-coil speaker is widely used, and a technique thereof is relatively mature. However, a shape thereof is not easy to be flatized due to its structure feature.
Main products of the electrostatic speaker in the market include hi-end earphones and loudspeakers. A functional principle of the conventional electrostatic speaker can be described as follows. A capacitor is formed by clamping a conductive vibrating film with two fixed electrode plates having holes, and by supplying a direct current (DC) bias to the vibrating film and supplying an alternating current (AC) voltage to the two fixed electrodes, the conductive vibrating film is vibrated due to an electrostatic force generated under a positive and a negative electric fields, so as to radiate a sound. The bias of the conventional electrostatic speaker has to reach hundreds to thousands voltages, and therefore an external amplifier with high price and great size has to be applied.
Regarding the electrostatic speaker, a U.S. Pat. No. 3,894,199 discloses an electroacoustic transducer structure shown as FIG. 1, which includes fixed electrodes 110 and 120 disposed at two sides. The fixed electrodes 110 and 120 have a plurality of holes used for distributing sounds. A vibrating film 130 is disposed between the fixed electrodes 110 and 120. A fixing structure 140 is formed by an insulating material and is used for fixing the fixed electrodes 110 and 120 and the vibrating film 130. The fixed electrodes 110 and 120 are respectively connected to an AC voltage source 160 through a transformer 150. When AC signals are transmitted to the fixed electrodes 110 and 120, potentials thereof are alternately changed, and the vibrating film 130 is vibrated due to a potential difference at the two sides, so as to generate a corresponding sound.
According to the above configuration, a sound pressure output has to be enhanced, so that an extra power device has to be applied, which can lead to a great size of the device.